funky heating duct

recently I encountered this situation in an old house. a duct had been run into an old unused brick chimney to transfer heat to the top level. though Ive not seen this before I did not see anything ‘wrong’ with it and actually considered it rather clever. I can only assume that whoever did this had the sense to seal above the exit duct upstairs (in the chimney)
…any opinions on this?
‘assume’ is probably a dirty word…perhaps I should have noted ‘this is non standard application and status of weather seal is unknown’…or some such statement.

Personally I would not want no dirty old chimney providing supply air into any area that I was living in. Are you sure that the duct was not inside the old brick flue. What did the top area of the brick flue look like did it have a metal duct take off. Ya know curiosity killed the cat but satification brought it back.

I’m assuming that the metal duct extends entirely through the chimney. If so, I don’t see a big problem. Unconventional yes.

to see if the duct extended upward through the whole chimney would have required pulling insulation and then observation would have been iffy. I would pretty much bet that it did not. I agree that lacking that…possible years of soot buildup could be introduced over time in the home. honestly I did not think of that…i have a problem considering stuff like that since i have no allergies and basically nothing affects me adversely…improvement needed in me there. so opinions? would anyone call this out as a defect? or just list it as a non standard apparently functioning condition (it was, heat was coming out the top) and recommend a look by a qualified HVAC tech?..or just figure it works, its cool…(kind of what I did)

If the metal duct was not inside the brick flue I personally would have called it out as a defect